Steam activation,characterisation and adsorption studies of activated carbon from maize tassels

In this paper, steam-produced activated carbon (STAC) from maize tassel (MT) was evaluated for its ability to remove basic dye (methylene blue MB) from aqueous solution in a batch adsorption process. The equilibrium experiments were conducted in the range of 50–300 mg/L initial MB concentrations at 30°C, for effect of pH, adsorbent dosage and contact time. The experimental data were analysed by Langmuir, Freundlich and Temkin isotherm models of adsorption. Freundlich adsorption isotherm was found to have highest value of R²(R²=0.97) compared to other models of Langmuir and Temkin having (0.96 and 0.95 respectively). STAC has a high adsorptive capacity for MB dye (200 mg/g) and also showed favourable adsorption for the dye with the separation factor (R_L<1) for the dye-activated carbon system. The kinetic data obtained were analysed using pseudo first-order kinetic equation and pseudo second-order kinetic equation. The experimental data fitted well into pseudo second-order kinetic equation, as demonstrated by the high value of R².     

Kinetic,equilibrium and thermodynamic studies for the sorption of metribuzin from aqueous solution using banana peels,an agro-based biomass

Banana peels were employed for the removal of metribuzin from aqueous solution. Sorption in the batch mode was optimized regarding pH, contact time, sorbent dose, initial pesticide concentrations, and temperature. The sorption data were fitted to pseudo-first-order, pseudo-second-order, intraparticle diffusion, Elovich, and liquid film diffusion model, the pseudo-second-order exhibiting best fit (R² = 0.9803). Of the four most common sorption isotherm models (Langmuir, Freundlich, Tempkin, and Dubinin–Radushkevich), the data followed the Langmuir isotherm with highest correlation. The maximum adsorption capacity was found to be 167 mg g^?1. Gibbs free energy, enthalpy, and entropy showed that the sorption was exothermic and spontaneous.     

Adsorption of methylene blue from aqueous solution by chemically treated water hyacinth

Water hyacinth (WH), an aquatic plant macrophyte, was investigated for its ability to perform as a suitable adsorbent for methylene blue (MB) from aqueous solution. The non-living biomass of WH was subjected to several chemical treatments, namely, washing with hot water, washing with hot dilute HCl, soaking in NaOH, soaking in HNO₃, and sulfonation. The system variables studied also include pH and MB concentration. The Langmuir isotherm was found to represent the measured adsorption data well except for WH soaked in NaOH, which was found to be better represented by the Freundlich isotherm. Values of the dimensionless separation factor, K _R, indicated that the adsorption systems in this study are all favorable. Values of the first layer of adsorption were calculated by the non-linear multilayer adsorption model, and the specific surface area values were found to be high and comparable to commercially activated carbons.     

Adsorptive removal of rhodamine B from textile wastewater using water chestnut (Trapa natans L.) peel: adsorption dynamics and kinetic studies

Water chestnut peel, an agricultural bio-waste, was used as a biosorbent for removal of rhodamine B (RhB), basic textile dye, from an aqueous solution. The effects of various experimental parameters were studied. The equilibrium data correlated well with a Freundlich isotherm (R² = 0.98–0.99) followed by a Halsey isotherm model (R² = 0.98–0.99) which indicated heterogeneity of the adsorbent surface and multilayer adsorption of RhB dye onto the water chestnut peel waste (WCPW). High correlation coefficients (R² = 0.99) together with close agreement between experimental q_e (0.4–1.7 mg g^?1) and calculated q_e (0.4–2.5 mg g^?1) suggested that the adsorption process followed pseudo-second-order kinetics, with k₂ values in the range of 52–3.4 × 10^?1 g mg^?1 min^?1 at different concentrations. The overall mechanism of adsorption was controlled by both liquid-film and intra-particle diffusions. The negative values of change in Gibb's free energy (?ΔG⁰ = 19.2–29.2 kJ mol^?1) and positive values of change in enthalpy (ΔH⁰ = 30.9–117.6 kJ mol^?1) revealed the process to be spontaneous and endothermic. WCPW was found to be an effective adsorbent for removal of RhB, a cationic dye, from an aqueous solution.     

Kinetic and equilibrium study of Alizarin Red S removal by activated carbon

Activated carbon has been applied for the adsorption of Alizarin Red S (ARS) from the waste water in a batch method to obtain high removal percentage. The influence of variables such as pH, temperature, ARS concentration, mass and size of adsorbent, and contact time on ARS removal percentage was investigated. Different kinetics, thermodynamics, and isotherm models were applied for fitting the experimental data. The adsorption process follows a pseudo second-order kinetic model with R ² of 0.98 and Freundlich, Tempkin, and Dubinin-Radushkevich isotherm models with high determination coefficients (R ²) of 0.91, 0.98, and 0.98, respectively. High enthalpy (positive value), Gibbs free energy (negative value), and high entropy values shows the feasibility and the endothermic spontaneous nature of the removal process.     

Adsorption of cationic and anionic surfactants onto organic polymer resin Lewatit VPOC 1064 MD PH

The adsorption of a cationic (CTAB, cetyl trimethylammonium bromide) and an anionic surfactant (SLES, sodium dodecylethersulfate) from aqueous solution onto organic polymer resin (Lewatit VPOC 1064 MD PH) was studied. A series of batch experiments were performed to determine the sorption isotherms of surfactants to organic polymer resin. The experimental studies were analyzed by Langmuir and Freundlich isotherms. Furthermore, the isotherm parameters, average percentage errors (ε) of model data, and separation factor (R _L) were calculated. Other factors influencing the adsorption capacity (contact time, adsorbent amount, and initial surfactant concentration) were also discussed. The experimental data fitted very well to the Langmuir equilibrium model in the studied concentration range. The calculated R _L values showed that the adsorption of both surfactants were favorable. Among the surfactants, CTAB showed higher adsorption capacity onto organic polymer resin compared to SLES (Q ⁰ = 250 and 34.36 mg g⁻¹, respectively).     

Kinetic and equilibrium models for the biosorption of Cr(III) on Streptomyces rimosus

This study focused on the biosorption of trivalent chromium onto mycelial bacterium (Streptomyces rimosus) biomass from effluent of tannery. The biomass was prepared by treatment with alkali. Fourier transforms-infra red analysis of the mycelial bacterial revealed the presence of carboxyl groups as possible binding sites. Experimental parameters affecting biosorption processes such as pH contact time were studied. Langmuir, Freundlich, and Temkin models were applied to describe the biosorption isotherms. The Langmuir model fitted the equilibrium data better than the Freundlich isotherm. The biosorption capacity of S. rimosus biomass for trivalent chromium was found to be 83 mg g^?1 at pH 4.8 and 3 g L^?1 biomass dosage, 300 min equilibrium time and 20°C. Kinetic evaluation of experimental data showed that the biosorption processes of trivalent chromium followed pseudo-second-order kinetics well.     

Pomegranate husk as an adsorbent in the removal of toxic chromium from wastewater

The use of a new sorbent developed from the husk of pomegranate, a famous fruit in Egypt, for the removal of toxic chromium from aqueous solution has been investigated. The batch experiment was conducted to determine the adsorption capacity of the pomegranate husk. The effects of initial metal concentration (25 and 50 mg l^?1), pH, contact time, and sorbent concentration (2–6 g l^?1) have been studied at room temperature. A strong dependence of the adsorption capacity on pH was observed, the capacity increased as the pH decreased, and the optimum pH value was pH 1.0. Adsorption equilibrium and kinetics were studied with different sorbent and metal concentrations. The adsorption process was fast, and equilibrium was reached within 3 h. The maximum removal was 100% for 25 mg l^?1 of Cr⁶⁺ concentration on 5 g l^?1 pomegranate husk concentration, and the maximum adsorption capacity was 10.59 mg g^?1. The kinetic data were analysed using various kinetic models—pseudo-first-order, pseudo-second-order, Elovich, and intraparticle diffusion equations—and the equilibrium data were tested using several isotherm models, Langmuir, Freundlich, Tempkin, Dubinin–Radushkevich, and Generalized isotherm equations. The Elovich and pseudo-second-order equations provided the greatest accuracy for the kinetic data, while Langmuir and Generalized isotherm models were the closest fit for the equilibrium data. The activation energy of sorption has also been evaluated as 0.236 and 0.707 kJ mol^?1 for 25 and 50 mg l^?1 chromium concentration, respectively.     

Copper (II) adsorption studies using models of synthetic humic acids

A polymer with characteristics similar to those of humic acids was obtained by synthesis reactions from oxidative polymerization in an alkaline medium using para-benzoquinone, hydroquinone and 4-aminobenzoic acid as precursors. Samples of natural and synthetic humic acid were used to examine the adsorption behavior of Cu²⁺ ions on these substrates. The mathematical models described by Langmuir and Freundlich equations were applied, yielding the maximum adsorption intensity values K′ (Langmuir), maximum adsorption capacity, b (Langmuir) and the adsorbent adsorption capacity, m (Freundlich). Based on solubility studies, pH 3 was selected for the development of the adsorption experiment. The Cu²⁺ ion presented a favorable adsorption, with RL (equilibrium parameter) responses in Langmuir isotherms falling within the desirable ranges.     

Adsorption of rhodium(III) from plating solutions by calcined gibbsite

Gibbsite calcined at 400°C (GB400) was prepared, and its ability to adsorb rhodium(III) was investigated. Optimal pH, effect of contact time, temperature, adsorption isotherms, and recovery percentage were evaluated. The optimal pH was 6.3. The adsorption equilibrium was achieved within 24 h. The adsorption rate was found to be of pseudo-first order. The experimental data were fitted to both the Freundlich (r = 0.90–0.93) and Langmuir (r = 0.94–0.96) equations. The amount of rhodium(III) adsorbed decreased with increasing temperature. Rhodium(III) being adsorbed from phosphate or sulfate plating solution was recovered using hydrochloric acid and sodium hydroxide solutions at 1, 10, and 100 mmol L^?1.     

Removal of Mo(VI) from aqueous solutions using sulfuric acid-modified cinder: kinetic and thermodynamic studies

Removal of Mo(VI) from aqueous solutions was investigated using cinder modified by sulfuric acid. Various parameters such as pH, agitation time, Mo(VI) concentration, and temperature have been studied. The maximum adsorption of Mo(VI) occurred at pH between 4.0 and 6.0. Kinetic studies showed that the adsorption generally obeyed a pseudo second-order model. The activation energy was 31.4?kJ?mol^?1, indicating that the adsorption process was governed mainly by interactions of physical nature. Furthermore, application of Langmuir and Freundlich isotherm models to the adsorption equilibrium data showed that the adsorption behavior obeyed the Langmuir model. The adsorption capacity was found to be 10.8?g Mo(VI)?kg^?1 adsorbent. Finally, thermodynamic parameters such as ΔH ⁰, ΔS ⁰, and ΔG ⁰ were also evaluated, which showed that the adsorption of Mo(VI) on the treated cinder was endothermic, entropy increasing, and spontaneous. In conclusion, the sulfuric acid-modified cinder was shown to be an inexpensive, effective, and simple adsorbent for the removal of Mo(VI) from water.     

Removal of congo red and basic violet 1 by chir pine (Pinus roxburghii) sawdust,a saw mill waste: batch and column studies

The efficiency of chir pine sawdust (CPS) for adsorptive removal of the dyes, congo red (CR) and basic violet 1 (BV), from aqueous solution was evaluated using batch and column studies. The equilibrium was attained in 60 min for CR and 45 min for BV. The adsorption of BV obeyed the Langmuir isotherm model while the Freundlich isotherm fitted the equilibrium data of CR adsorption. The Langmuir monolayer adsorption capacities (Q_o) of CPS for BV and CR were 11.3 and 5.8 g kg^?1, respectively. The kinetic data for CR were best fitted to the Lagergren pseudo-first-order model and for BV to the pseudo-second-order model. The intra-particle diffusion was found to be the rate-controlling step for CR adsorption, while the adsorption kinetics of BV were controlled by both intra-particle and liquid-film diffusion. The thermodynamic parameters indicated that the adsorption process was spontaneous and endothermic in nature. The adsorption activation energy (E_a) for CR (124 kJ mol^?1) implied chemical adsorption while that for BV (5.4 kJ mol^?1) indicated physical adsorption. An increase in the Thomas model constant (K_Th) with increasing flow indicated that for both dyes the mass transport resistance decreased during adsorption. Thus, CPS may be an efficient low-cost adsorbent for decolorization of dye-containing wastewaters.     

Removal of heavy metals from aqueous solutions using activated carbon prepared from Cicer arietinum

Removal of Cu²⁺, Cd²⁺, Pb²⁺, and Zn²⁺ from aqueous solutions by activated carbon prepared from stems and seed hulls of Cicer arietinum, an agricultural solid waste, has been studied. The influence of various parameters, such as pH, contact time, adsorbent dose, and initial concentration of metal ions on removal was evaluated. The activated carbon was characterized by FT-IR spectroscopy, X-ray diffraction, and elemental analysis. Sorption isotherms were studied using Langmuir and Freundlich isotherm models. All experimental sorption data were fitted to the sorption models using nonlinear least-squares regression. The maximum adsorption capacity values for activated carbon prepared from Cicer arietinum waste for metal ions were 18 mg g^?1 (Cu²⁺), 18 mg g^?1 (Cd²⁺), 20 mg g^?1 (Pb²⁺), and 20 mg g^?1 (Zn²⁺), respectively. The Freundlich isotherm model fit was best, followed by the pseudo-second-order kinetic model. Desorption studies were carried out with dilute hydrochloric acid for quantitative recovery of the metal ions and for regeneration of the adsorbent.     

Biosorption of Direct Yellow 12 from aqueous solution using green alga Ulva lactuca

The potential of commonly available green alga Ulva lactuca was investigated as viable biomaterials for removal of synthetic azo dye (Direct Yellow 12, DY-12) from aqueous solution. The results obtained from the batch experiments revealed that the ability of the U. lactuca to remove DY-12 from its aqueous solution was dependent on the dye concentration, pH, and algal biomass but less dependent on the particle size of the U. lactuca. The equilibrium conditions and kinetics of adsorption were investigated, and the adsorption kinetic was consistent with the pseudo-second-order model (R ²=1). The adsorption isotherm followed only the Freundlich model with a correlation coefficient R ²=0.99. This study demonstrated that the U. lactuca could be used as an effective biosorbent for the removal of DY-12 from its aqueous solution.     

Selenium content of rice,mixed plant foods and fish from Bangladesh

Static and dynamic adsorption studies of Co (II) ions have been undertaken at fixed pH and ionic strength taking binary biopolymeric beads of cross-linked calcium alginate and carboxy methylcellulose as biosorbents. The adsorption data were applied to Langmuir and Freundlich isotherm equations and various static parameters were calculated. The dynamic nature of adsorption process was quantified in terms of several kinetic constants such as rate constants for adsorption (K) and Lagergreen rate constant (K _ad). The influence of various experimental parameters such as solid-to-liquid ratio, pH, and temperature, the presence of salts and chemical composition of biopolymeric beads were investigated on the adsorption of cobalt ions.     

Equilibrium,kinetic, and quantum chemical studies on the adsorption of Congo red using Imperata cylindrica leaf powder activated carbon

Leaf powder of spear grass, otherwise known as Imperata cylindrica (IC), was used to prepare activated carbon. The Imperata cylindrica activated carbon (ICAC) prepared was used for the removal of Congo red (CR) dye from aqueous solution. Operation parameters such as initial dye concentration, contact time, adsorbent dosage, pH, and temperature were studied in batch systems. Equilibrium was attained in 150 and 180?min at lowest and highest concentrations, respectively. Maximum adsorption was observed at pH 3. Quantum chemical studies suggested that the protonation of aniline groups and minimal molecular size at planar geometry coupled with electrostatic interaction enhances the adsorption at low pH. Adsorption data were tested using pseudo-first-order and second-order reaction kinetics; the latter was found to be more suitable with a coefficient of determination of ≥0.99. The adsorption process fits Langmuir isotherm model better than the Freundlich model, with a maximum monolayer coverage of 313?mgg^?1. This study shows that ICAC is effective in removing CR dye from aqueous solutions.     

Modeling of adsorption kinetics and equilibria of acid dyes onto activated carbon in single- and binary-component systems

Adsorptive removal of Acid Blue 127 and Acid Yellow 17 from their single and binary solutions has been studied using powdered activated carbon (PAC). The dyes used extensively for dying of nylon fiber in textile industry are known as Nylomine Blue P-B (NB) and Nylomine Yellow P-4G (NY), respectively. Time-dependent results obtained from single-component system have been better predicted by two resistance diffusion model rather than homogeneous surface diffusion. The magnitudes of film- and intraparticle diffusion coefficients calculated from McKay equation are ～10^?9 and ～10^?15 m² s^?1, whereas surface diffusion coefficients have been estimated as ～10^?13 m² s^?1 using Vermeulen approximation. Experimental equilibrium isotherms have been evaluated by changing initial dye concentrations in the range of 0.02–1.00 of mmol L^?1. Freundlich isotherm parameters for individual solutions of the dyes have been used to predict their equilibrium behaviors in binary solutions by applying extended Freundlich model. Langmuir isotherm model and its extended form have also been fitted to the data for single- and binary-dye solutions, respectively. Thermodynamic functions derived from the temperature dependence of adsorption equilibrium constants in 298–318 K range show that adsorption processes are endothermic but spontaneous.     

Preparation and characterization of calcium alginate-based composite adsorbents for the removal of Cd,Hg, and Pb ions from aqueous solution

Composite adsorbent materials containing calcium alginate, clinoptilolite, and coal-derived humic acid were prepared. Humic acid (HA), clinoptilolite (CL), alginate (AL), alginate-entrapped humic acid (AL/HA), clinoptilolite (AL/CL), and humic acid/clinoptilolite (AL/HA/CL) samples were characterized. The effectiveness of the samples as adsorbents for the removal of cadmium (Cd), mercury (Hg), and lead (Pb) were studied in a series of batch-adsorption experiments. For the AL, AL/HA, AL/CL, and AL/HA/CL adsorbents, uptake versus time data were evaluated using two kinetic models, a linear and a non-linear pseudo-first-order and a pseudo-second-order model. The data for each metal ion on all adsorbents showed good correspondence with the pseudo-second-order kinetic model. The equilibrium data were fitted to Langmuir, Freundlich, Dubinin–Radushkevich, and Temkin isotherm models. The results show that a non-linear method seems more appropriate for obtaining isotherm parameters. The non-linear Freundlich and Langmuir models for Pb and Hg produced a best fit with high R ² value (0.99). For HA adsorbent, the equilibrium data for Cd removal better fit to the non-linear Dubinin–Radushkevich isotherm.     

pH dependence of copper adsorption in vineyard soils of Geneva

Copper adsorption by vineyard soils of the Geneva canton was evaluated by batch equilibration experiments in a pH range from 4 to 6. The adsorption curves fit significantly to Freundlich function log q = n log C + log K_f, where q is adsorbed Cu concentration on the solid phase and C is solution Cu concentration at the end of the equilibration time. Moreover, we found that Freundlich parameters n and log K_f are moderately correlated to pH, yielding the following equations: log K_f = 0.23 pH + 0.51 (R ² 0.59) and n = –0.12 pH + 1.06 (R ² 0.59). Such equations may be useful to predict Cu mobility for risk assessment studies.     

Removal of Janus Green dye from aqueous solutions using oxidized multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWCNTs) were oxidized and characterized by Fourier transform infrared spectroscopy. The adsorption characteristics of the oxidized MWCNT adsorbent were examined using Janus Green (JG) as adsorbate. In batch tests, the effects of pH, adsorbent dose, contact time, and temperature were studied. The maximum adsorption capacity was found to be 56 mg g^?1. The experimental data were fitted to the Langmuir, Freundlich, and Tempkin isotherm models, the first one being the most appropriate. Kinetic analysis showed that adsorption was most accurately represented by a pseudo-second-order model.